Abstract
Introduction
The wear performances of polyethylene in THA are influenced at a great extent by the manufacturing process. During the past decade, highly cross-linked materials have been developed with encouraging results in terms of wear, whereas another body of the literature has indicated potential catastrophic failures related to reduced fatigue properties and oxidation due to lipids adsorption and fatigue mechanism. Also, each of the materials available on the market has its own processing characteristics. Therefore, a specific evaluation is necessary for each of them. The aim of this retrospective study was to evaluate the wear properties of metal-back sockets using a first generation highly cross-linked PE in a consecutive series of primary THAs.
Materials
Between August 2005 and December 2007, 80 patients (80 hips) with a mean age of 62.7 ± 8.9 years were included. All patients had a 28mm CoCr femoral head articulating with a highly cross-linked insert (Highcross®, Medacta SA) that was 100 Mrads gamma radiated, remelted at 150°C, and ethylene oxide sterilized. The primary criterion for evaluation was linear head penetration measurement using the Martell system, performed by an investigator trained to this technique. Also, steady state wear was calculated. Functional results were evaluated according to WOMAC score.
Results
At the minimum of 5-year follow-up, complete data were available for analysis in 67 patients at a mean follow-up of 5.5 years (5.0 to 6.8). At the latest follow-up, the mean femoral head penetration measured 0.07 ± 0.23 mm/year (median of 0.09). The steady state penetration from one year onward representing wear was −0.03 ± 0.25 mm/year (median of 0.01). The WOMAC score significantly increased from 16.5 ± 5.93 preoperatively to 4.12 ± 5.5 at the latest follow-up (Mann-Whitney, p < 0.001). No case of polyethylene insert fracture was recorded, and no hip had signs of periprosthetic osteolysis on the acetabular or femoral side.
Discussion and conclusion
The minimal 5-year results of this retrospective study indicate that this highly cross-linked and remelted polyethylene had a low wear rate. The use of highly cross-linked inserts seem to be safe option provided that a minimal thickness of polyethylene is preserved. Longer-term results are needed to warrant that these mid-term data will generate less occurrence of osteolysis and aseptic loosening.
